Default [Q] help me i cant make call note 2

Hello

I own a note 2 gt-n7100 and I am running stock firmwar4.3 after upgrad is finished i can't make call and can't recive and bettry is not good and after press lock screen the screen take Seconds for open light Hope you'll help me.*
I want to downgrade for 4.1.2 is agood version
Thank You